qemu-sockets: add error propagation to inet_connect_addr

qemu-sockets: add error propagation to inet_connect_addr

perror and fprintf can be removed because all clients can now consume
Errors properly.  However, we'll need to change the non-blocking connect
handlers to take an Error, in order to improve error handling for
migration with the TCP protocol.

This is a minor degradation in error reporting for outgoing migration.
However, until 1.2 this case just failed without even attempting to
connect, so it is still an improvement as far as overall QoI is
concerned.

Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>